Plasmodium falciparum is the causative agent of the severest manifestation of human malaria. A unique characteristic of Plasmodium falciparum which allows it to cause such virulent disease is its ability to differentially utilize members of multi-gene families that are involved in the processes of cytoadherence and invasion. Variant expression of the Plasmodium falciparum Reticulocyte Binding Protein Homolog (PfRh) invasion ligands has been associated with alternative invasion pathways through differential erythrocyte receptor binding. We hypothesize that variant expression, in addition to parasite polymorphism in these critical invasion ligands, provides the parasite with a mechanism to adapt to different host environments as well as to evade immune responses. We have shown that naturally acquired immune responses exist which recognize the PfRh proteins and specific domains. We have also previously identified polymorphisms in these proteins which have been associated with altered invasion phenotype. The aim of this study is to generate transgenic parasite lines which will allow us to precisely address the contribution of domains and naturally occurring polymorphic alleles of the PfRh ligands on invasion, in the presence of polymorphic erythrocyte receptors or inhibitory antibodies. PUBLIC HEALTH RELEVANCE: The proposed research will provide a greater understanding of selective pressures which lead to emergence of polymorphic parasite genes, knowledge which could greatly inform both anti- malarial drug and vaccine design. Further, this research will contribute a detailed study of inhibitory immune responses raised against a family of invasion ligands which could be potential vaccine candidate antigens. Taken together, the aims of this study should provide valuable information as to the dynamics of parasite-host interactions in a disease endemic setting, and such information is critical when making and implementing malaria prevention and treatment policies.